Field of the Invention
The present invention relates to a forced flue heater that warms air using a heat exchanger through which combustion gas passes, and blows the warmed air into the room.
Background Art
Warm air heaters that blow warm air from an air outlet have been widely used to heat indoor areas. Such warm air heaters are categorized into one of two types: a heater that mixes combustion gas with air and blows the mixture as warm air into the room, or a heater that discharges combustion gas out of the room after the gas passes through a heat exchanger and warms air drawn from the room using the heat exchanger and blows the warm air (hereafter, a forced flue heater).
A forced flue heater includes a burner, which burns fuel to generate high-temperature combustion gas, a heat exchanger, through which the combustion gas generated by the burner passes, and a blower fan, which draws in air from the room and blows the air toward the heat exchanger. As the blower fan rotates, cool air is drawn in from the room and is blown toward the heat exchanger. The air is warmed by the heat exchanger. The warm air is then blown through a warm air outlet.
The forced flue heater that operates on the above principle is desired to maximize the amount of air that passes through the heat exchanger after blown from the blower fan, and to maximize the amount of air that is blown through the warm air outlet after heated by the heat exchanger. Thus, in many cases, the forced flue heater includes a partition defining an internal air channel, which contains the heat exchanger. The blower fan is installed at one end of the air channel to blow air into the channel. The other end of the air channel is open near the warm air outlet. This structure allows almost all the air that has been blown into the air channel to be warmed by the heat exchanger and to be blown through the warm air outlet.
In this forced flue heater, high-temperature combustion gas generated by the burner passes through the heat exchanger. This heats the heat exchanger to high temperature. If the heat exchanger is heated to an abnormally high temperature for some reason, the heat exchanger may crack. In this case, combustion gas inside the heat exchanger can leak outside through the crack, and may then move together with the flow of air blown by the blower fan and may be blown into the room through the air outlet. A forced flue heater (refer to, for example, Japanese Unexamined Patent Application Publication No. 2006-183916) may include a burner fan installed downstream from a heat exchanger to draw out the combustion gas and draw in fresh air into the burner, instead of a burner fan installed upstream from a burner to force fresh air into the burner. The burner fan installed downstream from the heat exchanger draws out the combustion gas to create negative (vacuum) pressure inside the heat exchanger. In this case, combustion gas inside the heat exchanger does not leak outside if the heat exchanger cracks.